It depends on the options on your WK2. If you have the larger brake callipers, (which I believe are standard on the Trailhawk) then 17" rims will not fit without some grinding or alteration. I've got a pair of 18" Mopar rims for off-road and only use my stock 20" rims on-road.
The largest tire size that will fit without modifications is 275/65R18, (which is about 32" tall and 10.8" wide). The only proper muddies I could find in this size were, Maxxis Bighorn MT-762s. There are several good A/T tires around (Cooper, Mickey Thompson, etc.) and you can get BFGoodrich MTs in a slightly smaller size, but they cost a fortune.
Hope that helps.